Wireless label-free electrochemical detection of cancer cells by MnO₂-Decorated polymer dots

The development of an optical biosensor for cancer diagnosis has encountered roadblocks and challenges because of some limitations including a high limit of detection (LOD), low sensitivity, time-consuming procedures, and expensive instrumentation. In this study, we designed a novel wireless electrochemical biosensor based on polymer dot-manganese oxide complexes (PD/MnO₂) that provided not only a fluorescence-based approach but also an electrochemical response for the detection of cancer cells on a coated surface. The electroconductive PDs exhibited strong fluorescent emission, which was quenched when the PDs were loaded onto MnO₂. This decreased the resistance of the biosensor. In the presence of the extracellular alkaline phosphatase (ALP) expressed by cancer cells and after the addition of 2-phospho-L-ascorbic acid (AAP), the PD/MnO₂ complex showed MnO₂ cleaving because of the formation of ascorbic acid (AA) as a result of the hydrolysis of AAP by ALP. This phenomenon caused the recovery of PD fluorescence and a change in the biosensor resistance, which was used as an indicator for cancer cell detection. The LOD of the PD/MnO₂ biosensor using the electrochemical approach was 3.98 cells/mL, whereas that of the biosensor using the fluorescence approach was 1995 cells/mL. Furthermore, the electrochemical signals could be collected by a wireless electronic device, which allowed real-time cancer detection directly using a smartphone. Thus, the wireless electrochemical biosensor developed in this study was suitable for cancer detection for biomedical and practical applications.